1. Field of the Invention
The present invention relates to an exchange-coupling film between an antiferromagnetic film and a ferromagnetic film and, a magneto-resistance effect element and a magnetic head using thereof.
2. Description of the Related Art
As a reproducing head in high density magnetic recording, study of a magnetic head (MR head) using a magneto-resistance effect film (MR film) is being proceeded. As an MR film, for example, a Ni.sub.80 Fe.sub.20 (at %) alloy (permalloy) and the like which shows anisotropic magneto-resistance effect (AMR) is well known. Since a change rate of magneto-resistance effect (MR change rate) of an AMR film is such small as about 3%, as an alternative MR film material, an artificial lattice film or a spin valve film such as (Co/Cu).sub.n which shows a giant magneto-resistance effect (GMR) is attracting an attention.
Since an AMR film consisting of such as a permalloy film or the like has a magnetic domain, it is important to eliminate Barkhausen noise due to that. Thus, various methods to transform an AMR film into a mono-magnetic domain is being investigated. As one of them, a method to control the magnetic domain of the AMR film into a particular direction by taking advantage of exchange-coupling between an AMR film, being a ferromagnetic material, and an antiferromagnetic film, is in use. As an antiferromagnetic material here, a .gamma.-FeMn alloy is traditionally well known (see, for example, specification of U.S. Pat. No. 4,103,315 and U.S. Pat. No. 5,014,147).
The above described spin valve film has a sandwich film consisting of a laminate structure of a ferromagnetic material layer/a non-magnetic material layer/a ferromagnetic material layer, and the GMR is obtained by pinning down magnetization of one ferromagnetic material layer. In pinning down of magnetization of one ferromagnetic layer material layer of such a spin valve film, a technology taking advantage of exchange-coupling between an antiferromagnetic film and a ferromagnetic film is prevailing. Also in this case, a .gamma.-FeMn alloy is dominantly used as an antiferromagnetic film.
However, there is a problem that a .gamma.-FeMn alloy is poor in its corrosion resistance and, in particular, is prone to be corroded by water. Therefore, when the .gamma.-FeMn alloy is employed, due to corrosion during processing steps of an MR element or a magnetic head or due to corrosion by moisture in the air, an exchange-coupling force with the MR element deteriorates with the lapse of time.
Besides, since a recent MPU in which its throughput is sped up generates heat in quantity, due to that even in a magnetic recording device such as an HDD, the temperature rises up to around 393 K. during operation. Therefore, the exchange-coupling film between an antiferromagnetic film and a ferromagnetic film, from the view point of reliability, is required to have an exchange-coupling force of 200 Oe or more at 393 K. In order to attain an exchange-coupling force of 200 Oe or more at 393 K., it is necessary not only to have high exchange-coupling force naturally at room temperature but also to be excellent in its temperature characteristics of the exchange-coupling force.
Concerning the temperature characteristic of an exchange-coupling force, the blocking temperature where an exchange-coupling force between a ferromagnetic film and an antiferromagnetic film is lost is desirable to be as high as possible. However, the blocking temperature of a .gamma.-FeMn alloy is 443 K. or less and its exchange-coupling force shows very bad temperature characteristic. Therefore, under the temperature environment described above, enough exchange-coupling force can not be obtained.
Thus, there are problems that an MR element or a magnetic head in which a .gamma.-FeMn alloy is employed as an antiferromagnetic film is likely to deteriorate in its characteristics during manufacturing process and, further, under the above described environment of operation temperature, enough long term reliability can not be obtained. To circumvent these problems, for example, in the specification of U.S. Pat. No. 5,315,468, a .theta.-Mn alloy such as a NiMn alloy which has a crystal structure of a face-centered tetragonal crystal system is disclosed to be used as an antiferromagnetic film.
In the above described gazette, it is disclosed that, when an antiferromagnetic film consisting of a .theta.-Mn alloy is employed, even in the higher temperature region, an exchange-coupling force between a ferromagnetic film and an antiferromagnetic film does not decrease. In addition, the present inventors have previously proposed an IrMn alloy having a crystal structure of a face-centered cubic crystal system as an antiferromagnetic film which has a high blocking temperature and a large exchange-coupling force, and is excellent in its corrosion resistance(Japanese Patent No. 2672802). As an antiferromagnetic film of the identical crystal structure, a .gamma.-Mn alloy such as a PtMn alloy or a RhMn alloy is known(see, specification of U.S. Pat. No. 5,315,468).
However, an operation environment of an MR element or a magnetic head, in which an exchange-coupling film between an antiferromagnetic film and a ferromagnetic film is used, is becoming more and more severe. For example, an environment temperature during operation tends to rise. In addition, accompanying high densification of recording density, narrowing tendency of a track and a gap is proceeding. Under these circumstances, it is required for the magnetization of, for example, one ferromagnetic material layer to be firmly pinned down. From these reasons, even an antiferromagnetic film consisting of such as an IrMn alloy, a PtMn alloy, a RhMn alloy can not necessarily be said that enough exchange-coupling force is obtained. Thus, there is a demand of an exchange-coupling film, which shows a large exchange-coupling force at room temperature and higher temperature region, between an antiferromagnetic film and a ferromagnetic film.
Further, although a sputtering method is generally employed to form an antiferromagnetic film, all the above described antiferromagnetic materials are consisting of Mn alloys difficult in manufacturing of a high density target. Therefore, there is a problem that control of film quality or purity of the antiferromagnetic film is difficult. Since a crystal structure of a face-centered cubic crystal system is formed in Mn-rich region, it is particularly difficult to produce a target of excellent quality. Deterioration of the film quality or the purity of the antiferromagnetic film can be cause to lower the exchange-coupling force of the ferromagnetic film. In addition, in an MR element or a magnetic head in which such an exchange-coupling film is employed, the antiferromagnetic film is likely to be badly affected from the other layer constituting them to be prone to be deteriorated in its exchange-coupling characteristics.